Air conditioning systems are currently commonplace in homes, office buildings and a variety of vehicles including, for example, automobiles. Air conditioning systems include a mechanical compressor that requires oil to properly function. During normal operation of the air conditioning system, a portion of the oil is entrained in the refrigerant and circulated through the air conditioning system. As such, in order to maintain the overall efficiency and efficacy of an air conditioning system, the refrigerant included therein may be periodically replaced or recharged.
Portable carts, also known as recover, recycle, recharge (“RRR”) refrigerant service carts or air conditioning service (“ACS”) units, are used in connection with servicing refrigeration circuits of air conditioning systems. The portable machines include hoses coupled to the refrigeration circuit to be serviced. During servicing of the air conditioning system, the oil entrained refrigerant from the air conditioning system is drained into an ACS unit, where the oil is separated from the refrigerant during a recycling/purification process. The old, separated oil is then drained from the ACS unit through a solenoid valve into a bottle so that an ACS unit technician knows how much oil needs to be injected back into the air conditioning system by the ACS unit. Providing the same amount of new oil back into the air conditioning system is important to ensure proper and efficient operation of the air conditioning system.
Previously, several methods have been used to measure the amount of oil drained from the ACS unit during a recovery process. A first commonly used method involves visual identification. The oil bottle of the ACS unit typically includes graduated markings to indicate the amount of oil in the bottle. The old oil is drained from the ACS unit into the oil bottle, and the user determines the amount of oil drained by visually inspecting the oil level in the bottle with reference to the graduated markings on the bottle. This method is generally low-cost, but relies on the user to correctly determine the amount of oil drained into the bottle, which is subject to user error.
Another conventional method uses a load cell to measure the weight of the oil bottle after the oil has been drained into the bottle. The system is configured with a controller to determine the weight of the oil drained by subtracting the weight of the bottle when empty from the weight of the bottle with the old oil. While this method is more accurate than reading markings on a bottle, load cells are expensive and delicate. As a result, ACS units having a load cell for the oil bottle are more costly to manufacture and maintain.
Furthermore, a load cell relies on the weight of the oil, rather than the volume. The density of oil significantly changes depending on oil temperature, and density is directly related to the conversion between weight and volume of the oil. Oil drained from the air conditioning system may be at a different temperature than the oil that is added to the air conditioning system by the ACS unit, which is typically at ambient temperature. Thus, if the ACS unit injects replacement oil having a weight corresponding to the weight of the oil removed, but the temperature of the replacement oil and the removed oil are different, a different volume of oil will be added to the air conditioning system than was removed.
It would therefore be desirable to provide an ACS unit having low cost and improved measurement accuracy of the volume of oil drained from an air conditioning system.